A graphics application, such as a computer-aided design (CAD) program, can be used to generate two dimensional and three dimensional representations of objects. A user can draw a shape typically using one or more lines, arcs or splines. Tools can be provided to a user to facilitate manipulating, sizing and replicating various components of a drawing. For example, a spline manipulation tool is provided in CAD software available from SolidWorks Corporation of Concord, Mass. A line that is tangent to a point on the spline that is to be manipulated is displayed to a user. The user can manipulate the tangent line. The spline is required to remain tangent to the tangent line, and is thereby modified in response to the user's manipulation of the tangent line. Subsequent manipulations to the spline, for example, using a tangent line at a different point on the spline, can interfere with earlier modifications to the spline, i.e., the modifications are not persistent.
Another example of a spline manipulation tool is provided in CAD software available from think3, Inc. of Cincinnati, Ohio. A line that is tangent to a point on the spline that is to be manipulated is displayed to a user at either an endpoint or a midpoint. The tangent line can be rotated to modify the spline, which stays tangent to the tangent line. The tangent line can also be lengthened or shortened, to lengthen or shorten the length of the spline that is substantially tangential to the tangent line. Modifications to the spline can persist during subsequent modifications to the spline at other points along the spline.